Why do some people think that parents are above criticism?

Because its the way societal tradition has infiltrated parental attitudes.

Ie: "Do as i say , not as i do"
"While youre under my roof....."
" You will do as you are told".
This attitude makes parents basically tyrants.
Which in itself is unethical.

One of the hardest things about being a parent is continually remembering that although we are expected to be perfect, we arent .
And that how society tells us be, we don't have to.